# Molecular detection of Orientia tsutsugamushi infection in bats from the China-Myanmar border

## TL;DR

Researchers found Orientia tsutsugamushi in bats in the China-Myanmar border, suggesting it may have originated from other animals or vectors.

## Contribution

This study reports the detection of multiple genotypes of Orientia tsutsugamushi in bats, providing new insights into its transmission and evolution.

## Key findings

- Orientia tsutsugamushi was detected in 7.32% of bat samples, with three genotypes identified.
- Ot DNA was found in multiple tissues of infected bats, with copy numbers ranging from 28.60 to 1069.76 copies/μL.
- Molecular clock analysis suggests Ot in bats emerged around 126 AD, later than in rodents and humans.

## Abstract

Orientia tsutsugamushi (Ot), the causative agent of tsutsugamushi disease (TD), has been detected in Muridae, Soricidae, Cricetidae, Canidae, Artiodactyla, and birds, as well as in its trombiculid mite vectors. However, to date, scarce reports have documented Ot infection in bats. TD is an ancient zoonotic disease transmitted through the bite of infected trombiculid mites. The global disease burden of TD, particularly in impoverished regions, warrants renewed attention and a reevaluation of public health strategies. In this study, we analyzed bat samples for Ot using nested PCR (nPCR) and real-time quantitative PCR (qPCR) for both qualitative and quantitative detection. Genetic evolution and divergence time of the detected Ot sequences were assessed using bioinformatics tools, including BioAider, Clustal X2, MEGA-X, and BEAST. Ot was detected in 7.32% (44/601) of bat samples by qPCR. At least three genotypes, including Karp, Gilliam, and Kato, were identified in both insectivorous bats (Hipposideros larvatus and Hipposideros armiger) and frugivorous bats (Rousettus amplexicaudatus and Cynopterus sphinx). Ot DNA was detected in multiple tissues, including heart, kidney, spleen, lung, rectum, liver, and brain, with median copy numbers ranging from 28.60 to 1069.76 copies/μL. Notably, divergence analysis suggests that Ot isolated from bats emerged around 126 AD, later than its appearance in rodents, humans, and chiggers (approximately 4140 BC), indicating that Ot infection in bats may originate from other animals or vectors. Our findings recommend ongoing monitoring of Ot in bats and their ectoparasites, which will provide a basis for risk assessment and guide strategies for the prevention and control of scrub typhus.

Orientia tsutsugamushi (Ot) is an obligate, intracellular bacterium and the causative agent of tsutsugamushi disease (TD) in humans. Ot is vectored by the biting of the larval life stage of infected mites. Scarce previous studies have reported Ot infection in bats. In this study, we identified at least three genotypes of Ot (Karp, Gilliam, and Kato) in four bat species, including H. larvatus, H. armiger, R. amplexicaudatus, and C. sphinx, along the China-Myanmar border. Molecular clock analysis suggests that Ot strains isolated from bats emerged long after the divergence of strains in rodents, humans, and chiggers, supporting the hypothesis that Ot isolated from bats likely originated from established mammalian or vector reservoirs. Our findings underscore the need for ongoing surveillance of Ot in bats and their associated ectoparasites to inform risk assessments and guide scrub typhus prevention and control strategies.